Conical screw mixer

Abstract

The present invention relates to a mixer (1) comprising a conical mixing tank (2), a mixing screw (5) extending within the tank (2) along an inner wall (4) of the tank (2), and a mechanism (6) for rotating said screw (5), said screw (5) being mounted on a rotating arm (7) about a central axis (A) of the tank (2). The tank (2) comprises an upper part (11), in which extends a first portion of the screw (5) having a first set of turns (17), a lower part (13), in which extends a second portion of the screw (5) having a second set of turns (18), and an intermediate part (12), located between the upper part (11) and the lower part (13), in which extends an intermediate portion (15) of the screw (5), said intermediate portion being without turns (15). Figure for the abbreviation: Figure 1

Description

Title of the invention: Conical screw mixer TECHNICAL FIELD OF THE INVENTION

[0001] The field of the invention is that of industrial mixers. There are several configurations of such mixers, which are generally used to achieve the homogeneous mixing of at least two products or to homogenize a product.

[0002] Among these mixers, the invention relates in particular to conical screw mixers. For simplicity, conical screw mixers may also be referred to more simply as "conical mixers" in this document.

[0003] Such mixers are often used for mixing or homogenizing granular, powdered, or even pasty products, particularly fragile products that must not be mechanically degraded during mixing. STATE OF THE ART

[0004] Generally, a conical screw mixer is equipped with a tank in the shape of an inverted cone (whose apex is oriented downwards) and at least one screw which extends from the apex to the base of the cone rotating on itself and also around the central axis of the cone.

[0005] This combined double movement has the effect of creating a complex continuous flow in the mixer, the product rising and falling in the mixer, with a tendency to rise in the center of the mixer and to fall back down along the conical wall.

[0006] This continuous circulation makes it possible to obtain a homogeneous mixture of the materials present in the mixer, in a relatively quick and very efficient manner.

[0007] When the outlet of the mixer, in the lower part of the conical tank, is opened, the mixture is drawn off under the effect (in part or in whole) of the spirals located at the bottom of the screw, which push the mixture located at the bottom of the cone through this outlet.

[0008] The general principle of such a mixer is described in document JPS58210835.

[0009] Examples of mixers of this type are shown in documents CN201755458 and CN2350117.

[0010] Documents CN201140050 and CN202155168 also present conical screw mixers, which have the particularity of comprising a long screw, which extends from the base to the top of the cone (i.e. from the top to the bottom of the mixer), and a shorter screw.

[0011] These mixers are very effective for producing a homogeneous mixture of solid products in powder or lump form, or even in paste form.

[0012] However, in the context of continuous or nearly continuous processes, in which product is continuously or frequently withdrawn from the mixer and in which If products are added continuously or frequently to the mixer, these mixers may present a disadvantage.

[0013] Indeed, although the withdrawn mixture is homogeneous, it is not possible to know for how long the products constituting this mixture have resided in the mixer.

[0014] However, some processes may require, in order to guarantee a reaction in the mixture, to ensure a regulatory heating time, etc., to guarantee that all products introduced into the conical screw mixer have resided there for a given period.

[0015] By knowing the flow rate, or more generally the quantities of the mixture withdrawn, and the tank capacity (or more precisely the quantity of products contained in the tank), it is of course possible to calculate an average residence time of the products in the tank. However, the complex mixing movements that take place within the tank do not allow for guaranteeing a minimum residence time in the tank for any product introduced into it.

[0016] In this context, the present invention aims to provide a conical screw mixer that solves this problem. Description of the invention

[0017] The present invention thus aims to remedy all or part of the disadvantages of the prior art mentioned above.

[0018] To this end, the invention relates to a mixer comprising a conical mixing tank, a mixing screw extending within the tank along an inner wall of the tank, and a mechanism for rotating said screw, the screw being mounted on an arm rotating about a central axis of the tank. The tank comprises an upper part in which a first portion of the screw extends, having a first set of turns, and a lower part in which a second portion of the screw extends, having a second set of turns. The tank also comprises an intermediate part, located between the upper and lower parts, in which an intermediate portion of the screw extends, which is without turns.

[0019] In the conical screw mixer according to the present invention, the screw has an intermediate portion that is without a spiral. The rotation of this smooth, spiral-free portion does not cause agitation in the mixer.

[0020] The applicant has observed that the functions of the screw can thus be divided vertically, in the tank.

[0021] Here and throughout the rest of this document, the mixer is assumed to be positioned so that the central axis (also called the principal axis) of the cone formed by the tank is vertical. The top of the tank corresponds to the base of the cone, and the bottom of the tank corresponds to the apex of the cone. The apex of the cone, at the bottom of the tank, forms also the outlet of the mixer through which the mixture formed in the mixer is drawn off.

[0022] Thus, in the upper part of the tank, the upper portion of the screw causes the products present in the tank to mix, as in a mixer conforming to the prior art. However, the downward and upward mixing flows caused by the rotation of the screw are limited to the upper part of the tank, to the heights where the screw has spirals.

[0023] In the lower part of the tank, in addition to possible stirring, the spirals of the lower portion of the screw drive the mixture (or participate in driving the mixture) out of the mixer, through its outlet.

[0024] In the intermediate section, the Applicant observed that the flow of the mixer was almost laminar. Thus, the descent of the product between the upper part of the tank (vertically, at the level of the upper portion of the screw) and the lower part of the tank (vertically, at the level of the lower portion of the screw) occurs regularly at a relatively homogeneous speed in any cross-section of this intermediate part of the tank (at the level of the intermediate portion of the screw).

[0025] The speed of descent of the mixture in this intermediate part depends on the mixing flow rate at the outlet of the mixer, and it accelerates progressively with the restriction of the section of the tank related to its conical shape.

[0026] It is thus possible to know quite precisely the time it will take for any sample of the mixture to travel from the bottom of the upper part of the tank to the top of its lower part. It is therefore possible to guarantee the time it will take for any element of the mixture to travel through the intermediate part. This time is also a certain minimum time for the transition of any element of the mixture within the mixer, because, assuming that this element is directly carried to the intermediate part of the tank after its introduction, and assuming that this element passes directly from the top of the lower part of the tank to the outlet of the mixer, it is nevertheless certain that it will have traveled through the intermediate part for this duration.

[0027] According to other optional features of the invention, which can be applied independently or in combination in various embodiments of the present invention: • the turns have a constant pitch; • the length of the intermediate portion is between one and five times said step; • the mixer includes a second mixing screw mounted on the rotating arm, said second screw extending only in the upper part of the tank; • the height, measured along the central axis of the tank, of the intermediate part, is between 10% and 30% of the sum of the heights of the upper part, the intermediate part and the lower part of the tank; • the volume of the intermediate part, is between 7% and 20%, for example 10%, of the sum of the volumes of the upper part, the intermediate part and the lower part of the tank; • the tank has a capacity between 1 m3 and 30 m3; • the mixer includes a device for regulating the flow rate of a mixture at the outlet of said mixer; • the mixer further includes a device for regulating the introduction of a first product and a second product into the mixer, the device for regulating the output flow rate and the device for regulating the introduction of the first product and the second product being configured so that over time, the introduction of the first product and the second product compensates for the quantity of mixture exiting the mixer; • the flow control device at the outlet of said mixer is configured so that the passage of any element of the mixture in the tank into the intermediate part takes place in a period of between 10 minutes and 30 minutes, for example between 13 minutes and 17 minutes, for example in 15 minutes; • the mixer includes a means of heating the products present in the tank, and / or a thermal insulation device between an internal volume of the tank and an external space of the tank. The invention also relates to a method for mixing two products comprising: • the supply of a mixer as described above, • the introduction of a first product and a second product (at least) into the upper part of the mixer tank, • the mixing of the first product and the second product, under the effect of the rotation of the upper portion of the screw, on itself and around the central axis of the tank, thus forming a mixture; • the transition, in laminar or quasi-laminar regime of the mixture, in the intermediate part of the tank; • the withdrawal of the mixture from the tank, at a flow rate controlled at least in part by the rotation of the lower portion of the screw.

[0028] In such a process, the first product may be a solid fraction extracted from insects and the second product may be insect cuticles, a fraction aqueous extracted from insects, or a mixture of insect cuticles and an aqueous fraction extracted from insects. BRIEF DESCRIPTION OF THE FIGURES

[0029] Other advantages, purposes and particular features of the present invention will become apparent from the following non-limiting description of at least one particular embodiment of the devices and methods of the present invention, with reference to the accompanying drawings, in which: • [Fig.1] is a schematic cross-sectional view of a mixer according to one embodiment of the invention; • [Fig.2] is a schematic view of the product flows in the mixer of [Fig.1], DETAILED DESCRIPTION OF THE INVENTION

[0030] The present description is given as a non-limiting example of an embodiment.

[0031] Fig. 1 represents a conical screw mixer according to an embodiment of the present invention.

[0032] The mixer 1 of the present invention comprises a tank 2. The tank 2, in which the mixing of products is carried out, is conical in shape.

[0033] Thus, the internal volume 3 of the tank 2 is delimited by internal walls 4 of the tank which form a cone, or strictly speaking a truncated cone (which is simply designated "cone" for simplicity).

[0034] The cone thus formed has a central axis A, which corresponds to the principal axis of said cone. The cone has a half-angle at its apex, referred to here as angle α, which depends on the embodiment considered. Tests of the present invention have been successfully carried out with a mixer whose tank has an angle of 17°, but many other values ​​are obviously conceivable.

[0035] The central axis A is, when the mixer is in use, vertical or at least substantially vertical. Therefore, throughout this document, the central axis A is considered to be vertical, with the base of the cone forming the top of the tank 2 and the apex of the cone being at the bottom of the tank 2.

[0036] The mixer includes a mixing screw 5 in the tank 2. The screw 5 extends along an inner wall of the tank, in the same orientation. In other words, the screw 5 forms the same angle α with respect to the central axis as the inner wall 4 of the tank 2.

[0037] The screw 5 is mounted to rotate on itself, that is to say, to rotate around its extension axis AL

[0038] A screw rotation mechanism 6, namely a geared motor assembly in the example shown, allows the screw 5 to be driven in rotation on itself.

[0039] The mixer also includes an arm 7. The arm 7 is perpendicular to the central axis A. The arm 7 is rotatable around the central axis A. The rotation of the arm 7 is ensured by a rotation device 8, namely a second geared motor assembly in the example shown.

[0040] The screw 5 is linked to the arm 7. In particular, the screw 5 is linked to one end of the arm 7.

[0041] In a known manner, the mixing of the products introduced into the tank is carried out, in whole or in part, under the effect of the rotation of the screw 5 on itself combined with the rotation of the screw 5 around the central axis A caused by the rotation of the arm 7.

[0042] The mixer also includes an outlet 9 from the tank 2. The outlet 9 is positioned at the bottom of the tank 2. It is through outlet 9 that the mixture M of the products introduced into the tank is drawn off. The mixture is then directed into a conduit 10.

[0043] In the context of the invention, three parts of the tank are distinguished, distributed vertically as follows. The tank 2 comprises an upper part 11, in which extends a first portion 14 of the screw 5, which has a first set of turns 17. The tank 2 comprises a lower part 13, in which extends a second portion 16 of the screw 5, which has a second set of turns 18. Finally, the tank 2 comprises an intermediate part 12, located vertically between the upper part 11 and the lower part 13. In the intermediate part 12, the screw 5 has an intermediate portion 15 in which said screw is without turns.

[0044] This configuration of the screw 5, and more generally of the mixer 1, results in the following operation for the mixer, illustrated in [Fig.2].

[0045] In the upper part 11 of the tank 2, the products, i.e. at least one first product PI and a second product P2 (and, depending on the mixture to be made, possibly other products), are mixed as in a conventional conical screw mixer. The mixture M of products PI, P2, is obtained by the mixing caused, at least in part, by the rotation of the screw 5 on itself (around its axis Al), and therefore by the effect of the first set of spirals 17, this rotation being combined with the rotation of the screw 5 around the central axis A.

[0046] This mixing causes flows in the upper part 11 of the tank 2, in particular downward flows Fl and upward flows F2, and more generally swirling flows in the upper part 11 of the tank 2. These flows cause a mixing of the products PI, P2. The mixture M is thus obtained.

[0047] In the intermediate part 12, the screw does not have a spiral. In this intermediate part 12, the intermediate portion 15 of the screw can typically be in the form of a smooth cylinder.

[0048] Generally, the thread of the screw 5 forms turns around said screw 5. Assuming that the pitch of the screw 5 (distance for the thread to make one turn of the screw) is Since the length of this intermediate portion is constant, it can be expressed as the number of turns (complete thread rotations) omitted. Thus, the length of the intermediate portion can be, for example, two turns (i.e., twice the screw pitch), one turn, three turns, four turns, or five turns.

[0049] In order to ensure all the functions of the mixer 1, in particular the mixing of the products, the guarantee of a minimum time of presence of the products in the mixer, and the withdrawal of the mixture, it can be provided that the intermediate part represents between 10% and 30% of the total height of the tank, that is to say the sum of the heights of the upper part, the intermediate part and the lower part of the tank.

[0050] In terms of volume, which is a more significant dimensioning parameter as explained below, the intermediate part can have a volume, for example, between 7% and 20% of the total capacity of the tank, namely the sum of the volumes of the upper, intermediate and lower part of the tank.

[0051] In this intermediate section 12, the mixture M flows from top to bottom in a regular and homogeneous manner, following a quasi-laminar flow regime. The laminar or quasi-laminar flows F3 are thus established in the intermediate section 12 of the tank 2. One can therefore speak of a "piston effect" which is produced in the intermediate section 12.

[0052] This transition of the mixture in the intermediate section 12 therefore occurs in a very predictable and repeatable manner. It is thus possible to determine, based on the mixing flow rate M exiting the mixer, the duration or residence time of the mixture in the intermediate section. This duration is equal to the volume of the intermediate section divided by the flow rate exiting the mixer.

[0053] It can therefore be guaranteed that the mixture has passed through the mixer for at least the time necessary to pass through the intermediate part, regardless of the difficulty in knowing the trajectory of each sample of the products in the upper part 11 and in the lower part 13 of the tank 2.

[0054] It is also possible to adapt the dimensions of the intermediate part, in particular its volume, by adapting its height, in order to obtain the desired transition time of the mixture in the intermediate part 11, which in fact is also the minimum residence time in the mixer for any product introduced into it.

[0055] In the lower part 13, the second set of turns 18 of the screw 5 can cause a certain mixing flow F4, but also causes (or assists) the withdrawal flow F5 of the mixture through the outlet 9 of the mixer.

[0056] The quantities of products PI, P2 introduced and the withdrawal rate of the mixture are advantageously controlled so that the level in the tank remains unchanged or oscillates between two given levels. In particular, it is ensured that the product to be mixed is always present in the upper part 11, at least as long as we intend to continue the production of mixture M.

[0057] To this end, a device for regulating the mixing flow rate at the outlet can be provided, such as a valve with a variable opening area, and / or a positive displacement pump at the mixer outlet. Simultaneously, a device for regulating the introduction of the products can be provided, linked to the flow rate regulation device at the outlet and / or to the product level in the tank.

[0058] Thus, the introduction of the first product and the second product (and any other product introduced) can compensate over time for the amount of mixture coming out of the mixer.

[0059] This regulation can be based on the total level of the product present in the tank, in order to keep it constant or varying it between predefined limits. Alternatively, this regulation can be based on the mass of the products present in the tank, in order to keep the total mass of these products constant or varying it between predefined limits.

[0060] Obtaining a certain minimum duration in the mixer can be advantageous or even necessary in many industrial processes.

[0061] This allows us to guarantee the complete realization of a reaction, for example.

[0062] In the example shown here, tank 2 includes a heating element in the form of a coil 19 surrounding the tank, through which a heat transfer fluid circulates (for example, water, particularly superheated water, steam, or oil at high temperature). Alternatively or in addition, tank 2 could be insulated, for example, by means of a double wall. These systems make it possible to heat or maintain the temperature of the products present in tank 2.

[0063] Heating the container can sterilize it, or simply reduce the microbial and bacterial load of the product. This heating, at a given temperature for a given time, may be necessary to comply with certain standards imposed in the food and animal feed industries.

[0064] It is therefore possible to use the mixer that is the subject of the present invention in order to make a mixture of products derived from insects.

[0065] The mixing carried out in the mixer can thus be part of a process comprising a step of separating the cuticles of the insects, so as to obtain the cuticles on the one hand and the soft part of the insects on the other hand, then a step of separating the soft part of the insects into an oily fraction, a solid fraction and an aqueous fraction.

[0066] This soft part separation step can be carried out in two sub-steps. Thus, in a first sub-step, the soft part of the insects is subjected to decantation using a two-phase decanter, so as to obtain a solid fraction and a liquid fraction. In the second sub-step, the liquid fraction is subjected to centrifugation, so as to recover an oily fraction and an aqueous fraction.

[0067] According to another embodiment, the soft part of the insects is subjected to decantation using a three-phase decanter (or "tricanter"), so as to directly obtain an aqueous fraction, an oily fraction and a solid fraction.

[0068] Once these three products have been obtained, three mixtures are particularly envisaged to be carried out in mixer 1: • a mixture of the cuticles and the solid fraction • a mixture of the cuticles, the solid fraction and the aqueous fraction, and • a mixture of the solid fraction and the aqueous fraction.

[0069] The insects used for this purpose may be mealworms (Tenebrio molitos). Other insects may be used, such as, by way of example, the black soldier fly (Hermetia illucens), or buffalo worms (Alphitobius diaperinus).

[0070] In the embodiment shown here, the mixer also includes a second mixing screw 20, which is mounted on the rotating arm 7. Like the screw 5, the second screw 20 rotates about its own axis of extension A2 and rotates about the central axis A of the tank 2 due to the rotation of the rotating arm 7. The second screw 20 can carry spirals along its entire length. The second screw improves the stirring and mixing performed by the mixer. In order not to compromise the quasi-laminar flow in the intermediate section 12 of the tank 2, the second screw extends only in the upper section 11 of the tank 2. For example, a free end 21 of the second screw is located at the bottom of the upper section 11.

[0071] The present invention being of particular interest in the context of the production of large quantities of a product, the following dimensions for the mixer can be given by way of example. Tank 2 can have a capacity of between 1 m³ and 10 m³.

[0072] Tank 2 may have, by way of example, a height between 1 m and 6 m, for example approximately 3.5 m. The term "approximately" means within 10%.

[0073] The height of the intermediate part can be between 25 cm and 2 m. The upper part is generally the part of the tank with the greatest height.

[0074] In the application mentioned above, namely the formation of an insect powder, the use of a mixer according to the present invention makes it possible to guarantee, in addition to the mixing of its ingredients, a maintenance at a temperature between 80°C and 92°C for a minimum period of 10 minutes.

[0075] More generally, in such a tank, it is possible, for example, to guarantee a transit time in the intermediate part 11 of the tank 2 (and therefore a minimum residence time in the mixer) of between 10 and 60 minutes. The mixer can be easily adapted, either by sizing the part intermediate or by the outlet flow rate, so as to have a minimum presence time lower or higher than these values. The duration can thus be adjusted according to the temperature of the mixture, depending on the objective pursued.

[0076] In the case of the insect-based mixtures mentioned above, this allows for a significant reduction in the population of certain heat-resistant pathogenic bacteria potentially present in the mixed products. The mixer can thus be the only machine in a production line to ensure this reduction at the required regulatory level. Alternatively, it can contribute to this reduction in conjunction with other machines in the production line that are heated.

[0077] The invention thus proposes a conical screw mixer which, in addition to producing a homogeneous mixture of products potentially fragile to mechanical action, guarantees a minimum presence time in the mixer for any product introduced into it. This makes it possible, for example, to guarantee a reaction, heating, or holding time for the products present in the mixer tank.

[0078] Nomenclature of reference symbols: • 1. Mixer • 2. Tank • 3. Internal volume of the tank • 4. Internal walls of the tank • 5. Mixing screw • 6. Screw rotation mechanism • 7. Arms • 8. Arm rotation device • 9. Tank outlet • 10. Conduit • 11. Upper part of the tank • 12. Intermediate part of the tank • 13. Lower part of the tank • 14. First portion of the screw (in the upper part) • 15. Intermediate portion of the screw (without a spiral) • 16. Second portion of the screw (in the lower part) • 17. First set of screw threads • 18. Second set of screw threads • 19. Heating medium (coil) • 20. Second mixing screw • 21. Free end of the second screw • A. Central axis of the tank cone • Al. Screw extension axis 5 • A2. Extension axis of the second screw 20 • a. Angle of the cone of the tank (half the angle at its apex) • PI. First product introduced into the tank • P2. Second product introduced into the tank • M. Mixture obtained from the products • Fl. Downward mixing flow in the tank • F2. Rising mixing flow in the tank • F3. Quasi-laminar flow in the intermediate part of the tank • F4. Mixing flow in the lower part of the tank • F5. Flow of the mixture being withdrawn through the tank outlet

Claims

Demands

1. Mixer (1) comprising: a mixing tank (2), the tank (2) having a conical shape; a mixing screw (5) extending within the tank (2), along an inner wall (4) of the tank (2); a mechanism (6) for rotating said screw (5) about itself; said screw (5) being mounted on a rotating arm (7) about a central axis (A) of the tank (2); the tank (2) comprising: an upper part (11), in which extends a first portion of the screw (5) having a first set of turns (17); a lower part (13), in which extends a second portion of the screw (5) having a second set of turns (18); characterized in that the tank comprises an intermediate part (12), located between the upper part (11) and the lower part (13), in which extends an intermediate portion (15) of the screw (5), said intermediate portion being devoid of a spiral (15).

2. Mixer according to claim 1, wherein the spirals have a constant pitch.

3. Mixer according to claim 2, wherein the length of the intermediate portion (15) is between one and five times said pitch.

4. Mixer according to claim 1 or claim 2, comprising a second mixing screw (20) mounted on the rotating arm (7), said second screw (20) extending only into the upper part (11) of the tank (2).

5. Mixer according to any one of the preceding claims, wherein the height, measured along the central axis (A) of the tank (2), of the intermediate part (12), is between 10% and 30% of the sum of the heights of the upper part (11), the intermediate part (12) and the lower part (13) of the tank (2).

6. Conical mixer according to any one of the preceding claims wherein the volume of the intermediate part (12) is between 7% and 20%, for example 10%, of the sum of the volumes of the upper part (11), the intermediate part (12) and the lower part (13) of the tank (2).

7. Mixer according to any one of the preceding claims, wherein the tank (2) has a capacity of between 1 m³ and 30 m³

8. ni. Mixer according to any one of the preceding claims, comprising a device for regulating the flow rate of a mixture (M) at the outlet (9) of said mixer (1).

9. Mixer according to claim 8, further comprising a device for regulating the introduction of a first product (PI) and a second product (P2) into the mixer (1), the device for regulating the output flow rate and the device for regulating the introduction of the first product (PI) and the second product (P2) being configured so that over time, the introduction of the first product (PI) and the second product (P2) compensates for the quantity of mixture (M) exiting the mixer (1).

10. Mixer according to claim 8 or claim 9, wherein the flow control device at the outlet of said mixer (1) is configured so that the passage of any element of the mixture in the tank (2) into the intermediate part (12) takes place in a period of between 10 minutes and 30 minutes, for example between 13 minutes and 17 minutes, for example in 15 minutes.

11. Mixer according to any one of the preceding claims, wherein the mixer (1) comprises a means for heating (19) the products present in the tank (2), and / or a thermal insulation device between a volume internal to the tank (2) and a space external to the tank (2).

12. A method for mixing two products comprising: - providing a mixer (1) according to any one of the preceding claims, - introducing a first product (PI) and a second product (P2) into the upper part (11) of the tank (2) of the mixer (1), - mixing the first product (PI) and the second product (P2), under the effect of the rotation of the upper portion (14) of the screw (5), on itself and around the central axis (A) of the tank (5), thus forming a mixture (M); - the transition, in laminar or quasi-laminar regime of the mixture (M), in the intermediate part (12) of the tank (2), - the withdrawal of the mixture (M) from the tank (2), at a flow rate controlled at least in part under the effect of the rotation on itself of the lower portion (16) of the screw (5).

13. A process according to claim 12, wherein the first product (PI) is a solid fraction extracted from insects and the second product (P2) is insect cuticles, an aqueous fraction extracted from insects, or a mixture of insect cuticles and an aqueous fraction extracted from insects.

Images